We live in the Sierra Mountains of Northern CA. We tow a 12,000 pound fifth wheel (Grand Design 303RLS). We tow mostly in CA, NV, OR, WA, MT, ID, and CO. We tow with a 2021 Chevrolet 3500 HD SRW L5P Duramax / 10 speed trans. The hottest I have seen the trans temp is 195 degrees, typically it runs at 147 degrees towing across Nevada in the summer for example. The highest ECT has been 220 degrees (pulling a relentless grade in Northern MT) typically it is 195 degrees. Literally everywhere we go is up or down grade. Assuming you do not have a mechanical problem with the engine (head gasket etc) or a transmission issue and are not loosing coolant it is most likely either poor air flow or a partially plugged radiator that is causing your issue (my educated guess as a retired mechanic not having the option to look at your truck in person). That truck is designed for commercial payload and delivery work not towing heavy, so it may be a challenge to keep it cool. Gear ratios may play a role. Go look at a new GM 2500 or 3500 diesel and note the size of the fan and radiator, you will understand. Please keep us posted on your solution to this issue and absolutely fix this before you head this way. That grade you showed is small compared to what we have out here.

I have seen auxiliary bug juice reservoirs w/ pumps plumbed into a spray nozzle in front of the radiator for additional cooling

I’ve been around the west twice with my C 4500 change, the oil more often, and I found the shell T6 works. The best on high mountain passes in Colorado. Now that I have 120,000 miles on my truck, I’m using royal purple changing out the oil every 7000 miles I’m at 30,000 pounds just keep your revs up and get that Jake the downhill side get the banks large oil cooler for the engine and then talk to Gary at Black cloud diesel. He has some real special injectors just for towing Keep that radiator fluid in good shape Check your vin make sure that the eighth digit is a 2 there are set up for towing. Starting my third trip around the United States in November this year, I love being retired

When I get into the mountains I run the cab heater on high with the fan on high. And open up the windows it will make a big difference on engine heat which also helps the transmission temperature.

Yall be careful! Love yall!

That was a struggle!! hope you get that thing fixed.

We took the scenic route to Rubicon Trail through the mountains. Boy was that a mistake haha. Towing 2 rigs on a gooseneck. Overheated going up, smoked all the brakes going down. Ended up going into 4 wheel LOW in the truck to keep from smoking brakes. Worked well.

I would say take a look at their called flex-a-lite fans and the radiator setup they got and I think you need to put an aftermarket transmission cooler and leave the one that's on there but they make them wear their aftermarket and they go under the truck or in the bed and they really help cool my dad used to truck pull that's why I know about these two things that was the only way we could keep the truck cool on the transmission and the motor

Thank u for sharing guys. Looking forward to more adventures New subscribers here

How does that truck not hold its own towing up that mountain? Geeze thats disapointing.

lol......being way overloaded tends to break stuff.........

I'm thinking an aux radiator and trans cooler, maybe under the truck along side of the drive line? About all you can do for the brakes is to NASCAR it, funnel air to the brakes with some fans to work even better at slow speeds. Does your truck have exhaust brakes?

I can't believe there are still (so called) car people that haul close to and over max gross that don't have the BIGGEST possible alloy radiator, trans cooler, added electric fan switched to come on 20° before max temp. That should be done before a hitch install especially if it's not a brand new truck......can anyone say Fan Shroud.

Always tow in 2nd gear with all chevys/gmc series trucks....I've been there with a 92 GMC 2500 350v8gaser....

I have a 2010 blue bird vision bus with the 6.7l cummins and the allison trans has a sweet vgt exhaust brake and had an idea after seeing a semi hooked to a 5th wheel camper thinking about pulling the bus body off and put a crew cab chevy body and put a flat bed kinda like yours on so I can haul a car on the back and have a goosneck hitch at the back to be able to tow my 35ft 5th wheel on the back just a thought I had think it would be pretty sweet! I have an 05 chevy 2500hd that I have a 12valve cummins nv4500 263xhd in that's my daily driver pulls the camper just fine but would like to be able to take another vehical with if possible. Sweet truck!! How long is your flat bed on yours?

We blow thru ocoee with a 43ft gooseneck like a sled on rails lol

Very awesome truck I want one for that same thing hauling my samurai and a trailer road lofe is where it is .lucky guys you are stay save driving

Its not a medium duty truck.. its a pickup engine in a truck that weighs 2x pickup

I have the same truck that is what your Exhaust brakes are for!!!

Does that not have an exhaust brake? I know the feeling living in Colorado and being 80 foot long, we can’t avoid the passes. I have an exhaust brake, but have to go very slow to make it work well.

I have a quick question for yall.. I am looking at an 07 top kick 5500 2WD Duramax, 289,000 on her, We would be towing a 17000 dry weight 45 ft toy hauler, Do yall think this truck would be adequate? Oh it is a 4 door as well, they are asking 17,000.00 Thanks ahead o time!! Great video but intense!! L.T. Dan

Your brakes should be fine by the way cuz once you got them cooled off he started moving the biggest thing is you don't want to let breaks it and stay hot you probably just took a little life out of them LOL but they should be just fine

Thanks for sharing tips. I'm thinking of trading up from 22 Duramax Dually to 5500. I heard the engine and transmission are very close to the same just de-tuned if that's right but stronger frame/suspension. Any advice?

Your way to heavy for what that truck is rated for. No exhaust brake ? Your lucky you didn’t get caught on the byway. Too heavy and too long your in the zone where the truck and trailer fall under commercial vehicle limits !

You endanger the general public.

U think bama roads r bad go to TEXAS. There the interstates r horrendous, especially I 35. Take out any dentures or partials, if u don't they'll be in pieces.

Cat or Duramax?

Hi whatcha up to hope all is well prayers 4 healing and unspoken also prayers 4 everyone and bless great healthy peaceful safe journeys and travels in the name of the Creator God and Yeshua/Jesus and the Holy Ghost Amen much honor and respect keep walking tall yall also transmission cooler and oil cool is needed if u don't have them if u r going do much mountain driving also jake brake would help too many blessings keep walking tall and keep on keeping on many blessings cool cool set up 🚌🌅🌌⛺🌄🏞🏖 👍👍💪🙂👍👍

Electric fans

That’s what you get for buying an automatic serves you right Bubba..